The Performance Of Aluminum Composite Foams Reinforced By In-situ Generated MgAl₂O₄ Whiskers

Aluminum composite foams reinforced by ceramic particles or short fibers have emerged as attractive structural and functional materials with high performance for applications in the aerospace and automotive industries.So far,the ceramic particles or short fibers reinforced aluminum composite foams were mainly developed and synthesized by ex-situ method.However,due to its inherent disadvantages,the method remitted many limitations for load bearing and energy absorption application and have no apparent improvements for the performance of foams.Thus it is meaningful to develop novel methods to prepare the aluminum composite foams.The in-situ fabrication is an ideal method which is has been widely developed to fabricate ceramic particles or short whiskers reinforced metal matrix composites?MMCs?.And that,MgAl₂O₄ spinel whisker is a desired reinforcement with the performance of high strength,high Young's modulus,high melting point and low coefficient of thermal expansion.More importantly,it has an extremely small mismatch?0.25%?between MgAl₂O₄ and Al lattices,which contributes to the excellent properties by improving the wettability between two phases.In this work,pure Al powders,Mg powders and H3BO₃ powders were used as the starting materials,and got the composite powders by ball milling pretreated with high speed for a long time.And the MgAl₂O₄ spinel whiskers were in-situ generated by the process of cold pressing and sintering.Then we prepared the precursor with the in-situ reinforcements.At last,the Na Cl particle were removed by heating in the water.We investigated the effect of sintering parameters on the morphology of MgAl₂O₄ spinel whiskers,and explored the influence of pore sizes,porosity and content of Mg on the mechanical property and energy absorption.The results show that the desired parameters of sintering are 750 °C and 2 hours.The in-situ MgAl₂O₄ spinel whisker exhibit a well combination interface with Al matrix.The diameter of whiskers with a regular hexagonal cross-section ranges from50 to 300 nm,and the aspect ratio is about 10-50,and the whiskers exist as three forms in the composite foams owing to the complicated structure of foams.As to the composite foams,the density and the plateau stress are decreasing with the increasing of porosity,the capacity of energy absorption is decreasing at the same time.On the other hand,the pore size have no obvious influence on the performance of foams.Compared with the pure Al foams?7.87,3.58,2.01 MPa?,the plateau stress?18.67,16.04,9.14 MPa?of composite foams with the porosity of 50%,60% and70 %increased by 137.23%,348.04% and 354.73% when adding 15 wt.% Mg as the starting material.Then the performances of Al composite foams reinforced by MgAl₂O₄ spinel whisker via the in-situ method have been greatly improved.